Yes, mainly to ensure board specifics are kept (serial, UUID, Win Key, LAN MAC ID etc) Also, often BIOS downloads are only partial files or missing NVRAM or other sections (if file same size), so you loose your NVRAM volumes too, depending on how you flash the mod BIOS into the board.

If you are using programmer, always modified a backup BIOS, if you are using software to flash in the mod then it depends on the software used (If FPT, always modify dump never stock download)

Thanks that was very helpful. I'll likely use software to flash, as I already modified the boot block, which was not reachable via software, and had to unsolder VCC to get it to flash. So not wanting to do that again if I can help it. but it does mean I have a good backup, just in case.

if there is flash software that would let me just flash a range instead of the whole rom, that probably be ideal. Still learning what's out there.

You're welcome! Since you unsoldered it you should have unlocked the FD while you have chip off the board, hopefully you did that! Programmer and SOIC8 test clip will let you program by address and you wont have to desolder again. You should consider picking up one of these clips, they only test $2.50 on ebay, let me know if you need an example link.

If the board is Intel based, and modern (last 8 years or so), then you can program via address as well with flashrom (I think) or Intel FPT

oh i have the sioc clips (Pomona) and used it for this.... i didn't unsolder the whole chip just the 3.3 v pin. . the problem was the 3.3v line was loading down the programmer as it was trying to drive the rest of the 3.3v logic on the board. ... so i just lifted the 3.3v pin on the chip and then hooked the clip up to it so i could program it in circuit.

The goal was to be able to upgrade a sandy bridge bios that had the bootblock blocked from writing via software to write in a boot block that supported ivy bridge. worked great.

I didn't realize at the time that id wanted to play with unlocking.... it is more of a recent interest, i can't believe the wealth of information out there on the topic.

plus, really, even if I wanted to do both at the time...making 2 changes at once might leave you not knowing which caused a problem

I see, maybe if you left in CMOS battery, or main power supply/battery, then you wouldn't have to do that either possibly.
You can still write BIOS region via FPT (Dump your own first, then mod, then flash back)
Backup >> FPTw.exe -bios -d biosreg.bin
Flash >> FPTw.exe -bios -f modbiosreg.bin

You need to download the correct ME System tools package, that matches your ME FW version, to get correct FPTw to use for this. If you need help with figuring that out and getting the ME System tools package with FPT let me know.